Chronic cocaine users have been shown in a number of studies to have persistent cognitive impairment even after cessation of cocaine use. In addition, they show patchy areas of decreased cerebral blood flow following such chronic use. Preliminary studies have demonstrated that the calcium channel blocking drug, nimodipine, tends to reverse decreased cerebral blood flow and metabolism as measured with positron emission tomography (PET). The same drug has ameliorative effects on the decreased amplitude of the P300 evoked potential, as measured by brain electrical activity mapping (BEAM). This evoked potential represents another measurement of cognitive impairment. Studies are proposed to answer the following questions; a) How rigorous is the effect of nimodipine? What are the proper doses and duration of treatment? The first question will be tested by a short-term double blind study comparing nimodipine versus placebo in patients who have sought treatment of chronic cocaine use. A slightly larger dose and longer duration of treatment will be employed than was used in the preliminary studies. Brain metabolism will be measured by PET scanning following Fl8 deoxyglucose (FDG) administration and brain blood flow following administration of 150-water. P300 amplitudes will be measured by the BEAM technique. b) Can the results from nimodipine be generalized to other calcium channel blocking drugs? Nicardipine will be first studied in an acute experiment measuring the same parameters following its intravenous administration. Should nicardipine also prove to be effective, other studies would follow using calcium channel blockers of different chemical and pharmacological types, such as verapamil and diltiazem. c) What are the effects of long term treatment? The goal here would be to treat patients who are abstinent for as long as six months, using blind controls. In addition to the laboratory measurements, clinical evaluation of success rates for maintained abstinence will be compared as well as questionnaire reports of other effects (?diminished craving). These studies should provide important answers regarding potential beneficial effects of this class of drugs in mitigating the deleterious effects of chronic cocaine use.